.TH std::ranges::mismatch,std::ranges::mismatch_result 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::ranges::mismatch,std::ranges::mismatch_result \- std::ranges::mismatch,std::ranges::mismatch_result

.SH Synopsis
   Defined in header <algorithm>
   Call signature
   template< std::input_iterator I1, std::sentinel_for<I1> S1,

             std::input_iterator I2, std::sentinel_for<I2> S2,
             class Pred = ranges::equal_to,
             class Proj1 = std::identity, class Proj2 = std::identity
   >                                                                  \fB(1)\fP \fI(since C++20)\fP
   requires std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
   constexpr mismatch_result<I1, I2>
       mismatch( I1 first1, S1 last1, I2 first2, S2 last2,

                 Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}
   );
   template< ranges::input_range R1, ranges::input_range R2,

             class Pred = ranges::equal_to,
             class Proj1 = std::identity, class Proj2 = std::identity
   >
   requires std::indirectly_comparable<
                ranges::iterator_t<R1>, ranges::iterator_t<R2>, Pred, \fB(2)\fP \fI(since C++20)\fP
   Proj1, Proj2>
   constexpr mismatch_result<ranges::borrowed_iterator_t<R1>,
                             ranges::borrowed_iterator_t<R2>>
       mismatch( R1&& r1, R2&& r2, Pred pred = {},

                 Proj1 proj1 = {}, Proj2 proj2 = {} );
.SH Helper types
   template< class I1, class I2 >                                     \fB(3)\fP \fI(since C++20)\fP
   using mismatch_result = ranges::in_in_result<I1, I2>;

   Returns the first mismatching pair of projected elements from two ranges: one
   defined by [first1, last1) or r1 and another defined by [first2, last2) or r2.

   1) Elements are compared using the given binary predicate p.
   2) Same as \fB(1)\fP, but uses r as the source range, as if using ranges::begin(r) as
   first and ranges::end(r) as last.

   The function-like entities described on this page are niebloids, that is:

     * Explicit template argument lists cannot be specified when calling any of them.
     * None of them are visible to argument-dependent lookup.
     * When any of them are found by normal unqualified lookup as the name to the left
       of the function-call operator, argument-dependent lookup is inhibited.

   In practice, they may be implemented as function objects, or with special compiler
   extensions.

.SH Parameters

   first1, last1 - an iterator-sentinel pair denoting the first range of the elements
                   to compare
   r1            - the first range of the elements to compare
   first2, last2 - an iterator-sentinel pair denoting the second range of the elements
                   to compare
   r2            - the second range of the elements to compare
   pred          - predicate to apply to the projected elements
   proj1         - projection to apply to the first range of elements
   proj2         - projection to apply to the second range of elements

.SH Return value

   ranges::mismatch_result with iterators to the first two non-equal elements.

   If no mismatches are found when the comparison reaches last1 or last2, whichever
   happens first, the object holds the end iterator and the corresponding iterator from
   the other range.

.SH Complexity

   At most std::min(last1 - first1, last2 - first2) applications of the predicate and
   corresponding projections.

.SH Possible implementation

   struct mismatch_fn
   {
       template<std::input_iterator I1, std::sentinel_for<I1> S1,
                std::input_iterator I2, std::sentinel_for<I2> S2,
                class Pred = ranges::equal_to,
                class Proj1 = std::identity, class Proj2 = std::identity>
       requires std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
       constexpr std::mismatch_result<I1, I2>
           operator()(I1 first1, S1 last1, I2 first2, S2 last2,
                      Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const
       {
           for (; first1 != last1 && first2 != last2; ++first1, (void)++first2)
               if (not std::invoke(pred, std::invoke(proj1, *first1),
                                         std::invoke(proj2, *first2)))
                   break;

           return {first1, first2};
       }

       template<ranges::input_range R1, ranges::input_range R2,
                class Pred = ranges::equal_to,
                class Proj1 = std::identity, class Proj2 = std::identity>
       requires std::indirectly_comparable<ranges::iterator_t<R1>, ranges::iterator_t<R2>,
                                           Pred, Proj1, Proj2>
       constexpr ranges::mismatch_result<ranges::borrowed_iterator_t<R1>,
                                         ranges::borrowed_iterator_t<R2>>
           operator()(R1&& r1, R2&& r2, Pred pred = {},
                      Proj1 proj1 = {}, Proj2 proj2 = {}) const
       {
           return (*this)(ranges::begin(r1), ranges::end(r1),
                          ranges::begin(r2), ranges::end(r2),
                          std::ref(pred), std::ref(proj1), std::ref(proj2));
       }
   };

   inline constexpr mismatch_fn mismatch;

.SH Example

   This program determines the longest substring that is simultaneously found at the
   very beginning and at the very end of the given string, in reverse order (possibly
   overlapping).


// Run this code

 #include <algorithm>
 #include <iostream>
 #include <ranges>
 #include <string_view>

 [[nodiscard]]
 constexpr std::string_view mirror_ends(const std::string_view in)
 {
     const auto end = std::ranges::mismatch(in, in | std::views::reverse).in1;
     return {in.cbegin(), end};
 }

 int main()
 {
     std::cout << mirror_ends("abXYZba") << '\\n'
               << mirror_ends("abca") << '\\n'
               << mirror_ends("ABBA") << '\\n'
               << mirror_ends("level") << '\\n';

     using namespace std::literals::string_view_literals;

     static_assert("123"sv == mirror_ends("123!@#321"));
     static_assert("radar"sv == mirror_ends("radar"));
 }

.SH Output:

 ab
 a
 ABBA
 level

.SH See also

   ranges::equal                   determines if two sets of elements are the same
   (C++20)                         (niebloid)
   ranges::find
   ranges::find_if
   ranges::find_if_not             finds the first element satisfying specific criteria
   (C++20)                         (niebloid)
   (C++20)
   (C++20)
   ranges::lexicographical_compare returns true if one range is lexicographically less
   (C++20)                         than another
                                   (niebloid)
   ranges::search                  searches for a range of elements
   (C++20)                         (niebloid)
   mismatch                        finds the first position where two ranges differ
                                   \fI(function template)\fP
